A light emitting diode (LED) is a semiconductor device that emits light using a recombination of an electron and a hole. The LED is widely used in various types of light sources of optical communication systems and electronic apparatuses.
A semiconductor light emitting device that emits light of a blue or an ultraviolet wavelength is formed by growing a gallium nitride (GaN) crystal. Such a gallium nitride crystal can be grown on a gallium nitride substrate, however, which is very expensive due to the difficulty of the process.
Accordingly, most of the general gallium nitride based light emitting diode is formed by growing it on a heterogeneous substrate. The heterogeneous substrate may be a sapphire (Al2O3) substrate, a silicon carbide (SiC) substrate, a gallium arsenide (GaAs) substrate and the like. Among them, most commonly used is a sapphire substrate.
The semiconductor light emitting device can be divided into a horizontal-type light emitting device and a vertical-type light emitting device depending on an arrangement structure of an electrode.
In the horizontal-type light emitting device, both electrodes are formed parallel to the growth surface of an epilayer because a sapphire substrate is an insulator. Since both electrodes of the horizontal-type light emitting diode are formed in the same direction, an electrode area above a predetermined size is required for wire bonding. In other words, the size of the light emitting diode chip should be greater than a pre-determined size. This makes it difficult to improve a chip production per wafer. Such a light emitting device with a horizontal-type electrode structure has a limitation in enhancing an optical output and a light emitting efficiency.
In the vertical-type light emitting device, both electrodes are formed on and under the light emitting diode, respectively. Accordingly, the vertical-type light emitting diode is more effective to improve an optical output and a light emitting efficiency.
FIGS. 1 and 2 are schematic sectional views illustrating a related art method for manufacturing a vertical-type light emitting device.
Referring to FIGS. 1 and 2, an n-type nitride layer 20, an active layer 30, and a p-type nitride layer 40 is sequentially formed on a sapphire substrate.
A p-type electrode layer 45 is formed on the p-type nitride layer 40, and a submount substrate 60 is formed on the p-type electrode layer.
After the n-type nitride layer 20, the active layer 30, the p-type nitride layer 40, the p-type electrode layer 45, and the submount substrate 60 is stacked sequentially as described above, the sapphire substrate 10 is removed. Thereafter, an n-type electrode 70 is formed under the n-type semiconductor layer 20 as shown in FIG. 2. As a result, a vertical-type semiconductor light emitting diode 80 is manufactured.
Here, the sapphire substrate 10 is separated and removed from the light emitting structure by irradiating a laser beam on bottom of the sapphire substrate 10 using a laser lift off (LLO) method.
However, since a laser beam of a wavelength below 250 nm is irradiated on the sapphire substrate 10 in general, a portion of the irradiated laser beam may penetrate the light emitting structure and affect even the p-type electrode. Therefore, the reliability of the semiconductor light emitting device may be deteriorated.
An etching and a mechanical polishing may also be used to remove the sapphire substrate 10. However, such methods also have the problem of causing damage to the nitride semiconductor layer.